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Ridge Capping Detail
last updated 30/12/08
Summary of this page

A ridge capping provides an effective watertight barrier, as well as an aesthetic finish to the cut ends of the sheet at the ridge and hip lines. Ridge cappings can be categorised into two styles; roll top ridge (also referred to as roll type ridge) and contemporary ridge capping.

Roll top ridge
Contemporary ridge

 
Roll Top Ridge
Download CAD versions of this flashing

The Design of the flashing
A roll top ridge is the most common form of ridge capping used today. The profile is typically a rollformed section which means the dimensions are standardised.
It is possible to produce a customised ridge capping, this is achieved by utilising tools that were used prior to the introduction of rollformers. If you are considering using a customised ridge capping you will need to consider that it will be restricted to short lengths and the cost would be considerably higher than a rollformed section.

Each suppliers ridge capping will be slightly different from the other manufacturers. It may also be possible for the profile to vary from a supplier on a state to state basis depending on the rollformer that was used to manufacturer the product. Therefore it is impossible to say there are standard dimensions for roll top ridge capping.


A typical ridge capping application
showing scribing.
What is meant when someone refers to a 350 roll top ridge?
The measurement 350 refers to the cut size of the steel that the profile is rollformed from. If you were to squash the ridge back to a flat piece of steel the width of the material would be 350mm. Some manufacturers produce additional sizes e.g. 405 roll top ridges. The additional material is used to extend measurement 'D'; this can be useful for providing greater protection from wind driven rain or when capping low pitch roofs. Instances may also arise where the top purlins are further apart and a standard ridge capping does not allow provide sufficient coverage. The Australian Standards call for a minimum overlap of 100mm of the roof sheeting.

Additional ribs are added to the profile to add strength and reduce any possible oil canning of the steel.

Measurements for the CAD detail available for download:
Width of the roll 'A' is 57mm.
The effective cover 'B' of the ridge is 260mm an the pitch 'C' is 30 degrees.
Measure 'D' is 95mm.
Break to suit the profile: 28mm @ 150 degrees.

Scribing
Scribing is the process of scalloping the break that match the roofing profile. Whilst this is not compulsory, it does give greater protection from water blowing back under the flashing and aesthetically adds to the detail.

Customising Roll Top Ridge
Whilst a rollformed roll top ridge is a standard size there are slight adjustments that can aid in the installation process. These adjustments are typically done on a folding machine. An example of this would be on a step pitch roof such as Tudor style. For this style roof the angle of a standard ridge 'C' would not be sufficient. Fasteners would pull the ridge in but in-between the fasteners the ridge would bludge outwards. To solve the problem, the angle of 'C' could be increased by refolding the break, eliminating this problem (request this at the time of ordering).

Ridge Capping detail type 1 - Roll Top Ridge

click to enlarge

click to enlarge

Download CAD versions of this detail
Contents: An array of roll top ridge details, including 15, 22, 27 & 30 degree sections (detail created with steel and timber purlins on different layers)

 

Contemporary Ridge Capping
Download CAD versions of this flashing

The Design of the flashing
Roll top ridge cappings are predominantly used on domestic dwellings using corrugated iron roof sheeting. The roll adds to the aesthetics of the roof and because they are rollformed sections, they provide a cost effective solution to capping the end of the sheets at the ridge and hips.

There are applications were an alternative to a roll top ridge is required:

  • Modern profiles which tend to be squarer in profile design are better matched with a non-roll ridge capping to compliment the roofing profile.
  • Commercial applications may require the ridge capping to have a larger coverage than what is available with a roll top ridge. Typically commercial roofing is a lower roof pitch and the additional coverage is required to ensure that protection is given to wind driven rain.

Whilst some contemporary ridge caps are rollformed, the majority are manufactured by folding. This is because
the sizes required are non-standard and tend to suit the application.

Additional ribs are added to the profile to add strength and reduce any possible oil canning of the steel.

Measurements for the CAD detail available for download:
A: 150mm
Break to suit the profile: 20mm

Scribing
As with a roll top ridge it is not compulsory that the break should be notched to suit the profile but on low pitch roofs it is always detailed as notched to suit the roofing profile, this aids in the prevention of wind driven rain entering the building.

Ridge Capping detail type 2 - Contemporary Ridge Capping

click to enlarge


click to enlarge

Download CAD versions of this detail
Contents: An array of contemporary ridge details, including 15, 22, 27 & 30 degree sections (detail created with steel and timber purlins on different layers)


Technical Resources
  1. Material Selection
  2. Acceptability of Drainage from an upper surface to a lower metal surface
For a complete list of BlueScope Steel Technical Bulletins click here
Resource Acknowledgements
Source: SteelSelect - author Richard Michael

Publication Details: November 05

Authors Disclaimers:  The information and advice contained in this article is of a general nature only, and has not been prepared with your specific needs in mind. You should always obtain specialist advice to ensure that the materials, approach and techniques referred to in this article meet your specific requirements. SteelSelect makes no warranty as to the accuracy, completeness or reliability of any estimates, opinions or other information contained in this article, and to the maximum extent permitted by law, SteelSelect disclaims all liability and responsibility for any loss or damage, direct or indirect, which may be suffered by any person acting in reliance on anything contained in or omitted from this document.